The present invention relates to apparatus and methods for defining optical signal paths in a photosensitive material. In one aspect, the present invention relates to an optical waveguide router that may be dynamically adapted by the use of a scanning system.
Routers are known in the art. A router is a device which routes and interconnects one, or many, network inputs to one or many network outputs through a variety of techniques. Optical routers are used to route incoming optical signals from one or more network inputs to one or more optical outputs. Optical fibres are typically used to apply and collect optical signals at the input and output ports. Methods known in the art for performing this routing on incoming optical signals include the use of patch panels, mechanical, thermo-optic, electro-optic and opto-electronic switching.
Patch panels have obvious drawbacks including requiring manual effort (i.e. human intervention) to alter the configuration of the patch panel. This manual manipulation to reconfigure the optical routing of signals in a patch panel can be quite time consuming and therefore costly. Moreover, patch panels do not allow for remote configuration of the routing signals.
Mechanical switches use electrical actuators, such as motors or solenoids, to physically move fibres or optical elements to alter to routing of the signal. While remote configuration of such a system is possible, it relies on mechanical translation, which is inherently slow and has limited configuration possibilities.
Devices using thermo-optic switches are remotely reconfigured through the use of materials which have indices of refraction which are temperature dependent. By changing the temperature (e.g. through the use of a dissipative element such as a resistor) the index of refraction of a waveguide can be altered, thereby allowing the construction of a switch to alter the path of an incoming optical signal. However, thermo-optic crosspoints built from such switches have a limited and fixed number of routing paths available since the waveguides are fixed resulting in a limited ability to reconfigure the crosspoint device. Moreover, the response time, that is the time taken to alter the refractive index at the thermo-optic crosspoint, is not sufficiently fast to allow for the deployment of the crosspoint device into a number of applications. Finally, to maintain the desired routing, the thermo-optic crosspoint requires that a waveguide or juncture be maintained at the required temperature otherwise the applied thermal energy will dissipate returning the thermo-optic switch""s index of refraction to its original, or initial, value. As such, the thermo-optic crosspoint, in response to power outage will lose all routing connections that existed prior to the outage.
Electro-optic devices operate in a similar manner to the thermo-optic devices, described above, except the change in refractive index is accomplished by the application of an electric field. These devices may be switched quickly with sufficiently large applied fields but are intrinsically sensitive to the polarisation of the incoming light. This polarisation sensitivity makes them unusable or very cumbersome to use in the majority of cases. In addition, these devices require patterned metal electrodes to apply the electric field which complicates the device""s manufacture.
An optical router can also be implemented through opto-electronic means by using optical-to-electrical converters followed by an electrical switch/router and then electrical-to-optical converters. Although this method does have advantages in some applications (such as the ability to do signal grooming, etc.) it requires a prohibitive number of components necessary to convert an optical signal into an electrical signal and back again. If wavelength division multiplexing (WDM) is used, the wavelengths must be separated and converted individually (with systems being introduced with up to 128 wavelengths and beyond on a single fiber, this is a severe drawback). Additionally, the optical-to-electrical and electrical-to-optical conversions can induce distortions in the signal which may be difficult or impossible to remove.
Accordingly, it is desired to provide a method and apparatus for the routing of an optical signal that addresses these shortcomings. More particularly, it is sought to provide a method and apparatus for the routing of optical signals which occurs in the optical domain, that can be dynamically reconfigured remotely, is not limited to a fixed number of routing paths and which may have a fast response time enabling wide deployment of the routing method and apparatus.
The present invention incorporates a photosensitive material, wherein the material changes between a first state and a second state when exposed to one or more particular wavelengths or wavelength bands of electromagnetic radiation. The change in state of the material results in a change of the material""s refractive index at a wavelength or wavelengths different from that of the exciting light. This change in the index of refraction can be used to form a waveguide allowing the propagation of an optical signal. The waveguide may be written by exposing the photosensitive material to electromagnetic radiation to change the material""s state and hence to route or switch optical signals. Note that, depending upon the material, a plurality of states and/or state changes may be possible.
Photosensitive materials have the property that, when irradiated by electromagnetic radiation, usually in the near visible or visible spectrum, the material will undergo a photochemical reaction, initiated by the photons, changing the material""s state. This new state may be stable and require a reverse photochemical reaction, normally at a different wavelength, to change the material back to its initial state. Alternatively, the material may be unstable or metastable and decay thermally to the initial, or ground, state after a period of time. Often this thermal intermediate state can also be photochemically driven back to the ground state. The electromagnetic absorption spectrum of the material is altered by this change of state. A photorefractive material is any material, upon exposure to electromagnetic radiation undergoes any type of process that results in a change in the index of refraction to incident light. One suitable photosensitive material is a photochromic material. The change in spectral absorption, which defines photochromism, is related to changes in the dielectric constant and hence index of refraction through the well known Kramers-Kronig relations.
Where a photochromic material is used, the change in spectral absorption directly allows for the construction of an optical attenuator.
In general, a material which reacts to light, be it photochromic, photorefractive, phototropic, etc., is referred to as being photosensitive.
The preferred embodiment incorporates a photosensitive material, such as Bacteriorhodopsin (bR), in the waveguide layer. When bR is illuminated with a radiation source of a first wavelength, it moves from a ground state, having an initial index of refraction to an active state exhibiting an altered index of refraction. Thus, a waveguide layer containing bR (or similar material) may be used to route optical signals in the plane of the layer. Portions of the waveguide layer illuminated by a radiation source of a first wavelength by, for example, a laser beam which traces a path on the waveguide layer or by a light source coupled with a mask, will exhibit an altered index of refraction different than that of the surrounding, non-reacted, material. In the case of bR, the index of refraction in the active state will be increased for writing wavelengths shorter than the ground state absorption peak. As such, a routing path can be created which exhibits properties similar to that of an optical fibre (that is an interior core of high index of refraction materialxe2x80x94in this case containing bR in its active statexe2x80x94than the surrounding claddingxe2x80x94in this case containing bR in its ground state). An optical signal received at an input port can then propagate through this routing path formed of reacted bR to a selected output port. Alternatively, if longer wavelengths need to be routed, the outside of the core can be delineated by suppressing the index of refraction in these areas using the same methods as above since, for wavelengths longer than the ground state absorption peak, the index of refraction of bR is reduced in the active state. This would be the case for wild type (WT) and current mutant forms of bR when applied to the optical transmission bands at 1310 nm and 1550 nm. (See diagram 33.3 I in the CRC Handbook of Organic Photochemistry and Photobiology, CRC Press, 1995, the contents of said Handbook hereby incorporated herein by reference). The routing path created by illuminating a portion of the waveguide layer can be erased by illuminating at least the previously exposed areas by a second wavelength of radiation which causes the photochromic material to undergo the reverse photochemical reaction. In the case of bR the photochemical reaction is photopolymerization.
In one aspect of the invention there is provided an optical router comprising: a waveguide layer; an optical input coupled to the waveguide; at least one optical output connected to the waveguide, the waveguide layer comprising a photosensitive material which has one index of refraction for an optical signal in a first state and a different index of refraction in a second state; and a route writing system emitting radiation to initiate a forward photosensitive reaction in the photosensitive material between the input and the at least one optical output.
In another aspect of the invention a method of routing an optical signal comprising the step of: initiating a photosensitive reaction in an interconnect material interconnecting at least one optical input and at least one optical output from a first state that substantially inhibits an optical signal from propagating from the input to the output to a second state which allows the propagation of the signal from the at least one input to the at least one output; and transmitting an optical signal through the interconnect material in the second state from the optical input to the optical output. This material may, in the first state, have a first index of refraction and in the second, a different index of refraction. The transformation from the first state to the second state may be responsive to routing information received from an external signal or taken from the optical signal that is to be routed.
In another aspect of the invention an optical waveguide system is disclosed. The optical waveguide system comprising: a photosensitive material; an input in communication with the photosensitive material; a plurality of outputs interconnected to the input by the photosensitive material; and a scanner for initiating a photosensitive reaction in the photosensitive material from a first optically non-transmissive state to a second optically transmissive state. The optical waveguide system may, in the first state, have a first index of refraction and in the second state have a second, higher, index of refraction. The optical waveguide system may, in the first state, have a first index of refraction and in the second state have a second, lower, index of refraction. Moreover, the photosensitive material may incorporate Bacteriorhodopsin.
In another aspect of the invention there is provided an optical waveguide system comprising: at least one optical input; at least one optical output; a waveguide layer composed of one of Bacteriorhodopsin, visual rhodopsin, chloroplast and photosynthetic reaction centres wherein the waveguide layer inhibits propagation of an optical signal in a first state and allows propagation of an optical signal in a second state; and a radiation source to irradiating the waveguide layer causing the waveguide layer to shift from the first state to the second state allowing an optical signal to propagate from the at least one optical input to the at least one outputs. The optical waveguide system may, in the first state, have a first index of refraction and, in the second state, may have a second, higher, index of refraction. The optical waveguide system may, have a first index of refraction and, in the second state, may have a second, lower, index of refraction.
In another aspect of the invention there is provided a waveguide system incorporating a material with a property of the material being at least one of: photorefractive and photochromic. The waveguide may incorporate one or more of the following materials: Bacteriorhodopsin, visual rhodopsin, chloroplast and photosynthetic reaction centres.
In still further aspect of the invention there is provided an optical switch incorporating a material with a property of the material being at least one of: photorefractive and photochromic.
In still further aspect of the invention there is provided an optical attenuator incorporating a material with a property of the material being at least one of: photochromic and photorefractive.
In a still further aspect of the invention there is provided an optical router comprising: a waveguide layer incorporating a photorefractive material; a route writing system for irradiating portions of the waveguide layer to change the index of refraction of the irradiated portions.
An optical switch is another aspect of the invention. The optical switch comprising: an optical input; an optical output connected to the optical input by a photosensitive material; the photosensitive material having a first state with a first index of refraction and a second state with a second index of refraction; and a scanner for initiating the photosensitive reaction in the photosensitive material from the first state to the second state.
A still further aspect of the invention is a method of routing an optical signal comprising: writing a routing path in a waveguide layer incorporating a photochromic material by irradiating portions of said waveguide layer to change the index of refraction of said waveguide in said irradiated portions; and transmitting said optical signal through said routing path.
A still further aspect of the invention is an optical attenuator. The optical attenuator comprising: an input port; an output port; a waveguide layer interposed between the input and output ports, the waveguide layer incorporating a material having a first index of refraction in a first state and a second index of refraction in a second state; a radiation source for causing the material to change from the first state to the second state; and a controller to control the radiation source to selectively irradiate a portion of the waveguide layer to create a routing path from the input port to the output port providing lateral optical confinement and attenuation of an optical signal transmitted along the routing path in the waveguide layer. The controller of the radiation source may be arranged to attenuate a signal in at least one of the following ways: adjusting an alignment of said routing path relative to the input port; adjusting an alignment of said routing path relative to said output port; incorporating specific geometry in said routing path; adjusting a guide strength of said routing path; adjusting a cross-sectional area of said routing path. Again, the transformation between states may be initiated by a scanner. Alternatively, the transformation may be initiated by an irradiated optical mask.
A still further aspect of the invention is a method for attenuating an optical signal, the method comprising: irradiating a path between an optical input port and an optical output port in a waveguide layer incorporating a photosensitive material, wherein the irradiated path in the waveguide layer displays an index of refraction different from the index of refraction in portions of the waveguide layer not irradiated such that an optical signal transmitted between the optical input port and the optical output port along the irradiated path is attenuated; and transmitting an optical signal from the optical input port to the optical output port along the irradiated path in the waveguide layer.
Employing this device allows for a dynamically reconfigurable routing, attenuating or switching device that does not require a substantial number of components. Moreover, the invention provides a method and apparatus for the routing of an optical signal which occurs in the optical domain, can be dynamically reconfigured remotely, is not limited to a fixed number of routing paths and which may have a fast response time enabling wide deployment of the routing method and apparatus.
Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.